There _____ no hospitals in my town sixty years ago. [ ]
A. is
B. was
C. are
D. were
答案:D
已知点P为圆x2+y2=4上的动点,且P不在x轴上,PD⊥x轴,垂足为D,线段PD中点Q的轨迹为曲线C,过定点M(t,0)(0<t<2)任作一条与y轴不垂直的直线l,它与曲线C交于A、B两点。
(1)求曲线C的方程;
(2)试证明:在x轴上存在定点N,使得∠ANB总能被x轴平分。
京派